Does anybody know a good PS1 game (nostalgia of course)

What kinds of games are you looking for?
Some of the best RPGs for the system are:

Final Fantasy Tactics
Suikoden 2
Saiyuki: Journey West
Valkyrie Profile

Test Drive Off-Road 3

I loved this game so much :D but one time I borrowed it to my friend and after 1 week he gave me scratched CD ;_; .

Alundra was good *.*

MechWarrior 2
Though the PC version was better, the PS1 Port was still fun :)

my small ps1 collection
alundra 1
alundra 2
command & conquer retalation
crash bandicoot 2
fear effect 2
final fantasy origins
final fantasy anthology
final fantasy 6
final fantasy 7
final fantasy 8
final fantasy9
front mission 3
g-police
grandia
guilty gear
in cold blood
star ocean the second story
wild arms
x-men mutant academy 2
and wantlist has over 100 games for ps1 alone

Final Fantasy VII, VIII, IX
Crash
Tekken
Medievil
Ape Escape!!!

Twisted metal and Fighting Force were both good ones. There was also frogger and q-bert.

Legend of Dragoon
Legend of legaia
metal gear solid 1
koudelka (i think it's from ps2 don't remember)
final fantasy tactics

Chrono Cross
Bloody Roar
Legend of Legaia
Legend of Dragoon
Medievil
Ape Escape
Omega Boost
Eternal Eyes

Just a few games I played as a kid (minus Legend of Dragoon and Medievil, I only played the demo of Dragoon in Walmart and the demo of Medievil in the Playstation Underground discs).

Probably already suggested, but Symphony of the Night

X-Men vs. Street Fighter

Puzzle Quest is a must-play on the original PSP.

Medal of Honour, Medal of Honour Underground, and Dino Crisis 1&2 Resident evil 1-3, Crash Bandicoot 1-3, Spyro 1-2, Siphon Filter, But my all time favorite PS1 Game of all time is Heart of Darkness.

Super Mario Kart!

pandemonium

Metal Gear?
Crash Team Racing! xD
Bishi Bashi? "Party" games are fun to play with your friends

Jade Cocoon? Legend of Dagoon?

PaRappa the Rapper
https://en.wikipedia.org/wiki/PaRappa_the_Rapper

Team Buddies
Hogs of War
Army Men series

Granted first two are better in multiplayer but fun nonetheless.

Already 5 pages, so I won't read back, sorry - but old Disney games (Lion King, Hercules, Tarzan) were fantastic, I totally recommend them :)

Mickey's Wild Adventure

Harvest Moon Back to Nature :D

Brigandine: The Legend of Forsena
Still waiting for Brigandine 2

Wipeout 2097, and also Legacy of Kain (though i forget which one were the best of Blood Omen or Soul Reaver, but leaning on it being Soul Reaver..) :)

Here's my top picks. Not much RPG as they are time sink.
Brigandine is something like Dragon Force for the Sega Saturn. I quite enjoyed it

Brave Fencer Musashi
Brigandine - Legend of Forsena
Bust A Groove
Crash Bandicoot
Galerians
Harvest Moon Back to Nature
PaRappa the Rapper
Syphon Filter
Trap Gunner
Um Jammer Lammy

Even though I personally never played it, Legend of Dragoon seems to be one of the best games ever released for the PS1